This invention relates to telephone service lines, and more particularly to a novel method and means for selecting and testing unused telephone lines at points remote from a central office.
As a general rule, most telephone companies in metropolitan areas utilize a plurality of so-called central offices, each of which services a large number of telephone circuits for individual subscribers. Each telephone circuit, such as for example the circuit to an individual residential subscriber, includes two telephone lines or cables, one of which is known as the ring line, and the other which is known as the tip line. The circuit which services a given subscriber's telephone can also include a third line known as a ground line.
Most of the pairs of tip and ring lines emanating from a central office are connected to respectively different telephones; but others of such pairs constitute unused lines which are available for connection to the telephone of a new subscriber. This present invention is concerned only with unused pairs of telephone lines.
In order to connect a new subscriber to a pair of unused telephone lines, it is customary for a worker to travel to the premises of the new subscriber, and to install the telephone by climbing a nearby telephone pole to investigate one-by-one the numerous pairs of telephone lines which pass through an overhead cable. The worker employs a conventional instrument for testing each pair of lines, and if a dial tone is heard, the existence of the tone indicates that that particular pair of lines (tip and ring) are in use. On the other hand, if the worker finds a pair of lines that do not exhibit a dial tone, he realizes that, presumably, he has found an unused pair of lines which can then be connected to the new subscriber's telephone.
However, before connecting the new telephone to the selected pair of tip and ring lines, the worker must first test the lines to make sure that they have not become accidentally shorted or severed at some point between the subscriber's home and the central office, thus making sure at the outset that the pair of lines are operative, though unused. Heretofore in order to conduct such a test it was customary for the worker to call someone at the central office, and to have that person test the selected pair of lines to make sure that the new subscriber's phone can be rung up, or rung through, the central office. This is a time consuming and expensive operation.
Instruments are available for testing telephone lines, but both the equipment and the purpose are different from the present invention. U.S. Pat. No. 4,350,849, for example, discloses a line testing device which utilizes a varying impedance to test whether or not a subscriber line is satisfactory or unsatisfactory because of some failure. However, the testing is conducted from the telephone central office, rather than in the field at a point remote from the office; and the testing elements are located at the central office, and are not used for testing unused telephone subscriber lines.
U.S. Pat. No. 3,951,248 discloses a line status indicating device which is located on the subscriber's premises, but it is not used for testing unused telephone lines. It merely indicates at one extension phone, when another extension phone on the same line is being employed.
U.S. Pat. No. 4,513,179 discloses a loop testing device, but it is designed specifically for using a jack with a wall socket, which terminates a telephone or other electrical circuit. The device disclosed in U.S. Pat. 3,976,849 also is designed for a purpose which is entirely unrelated to this invention, since the device in this patent is intended to be substituted in place of a telephone. The U.S. Pat. No. 4,596,904 has for its purpose the identification of individual telephone lines at the end of a trunk cable, but it functions only in connection with a closed system, for example an in-house PBX system. This system and method cannot be applied for detecting the presence of unused pairs of telephone lines as between a subscriber's telephone, and a remote central office main frame.
It is an object of this invention, therefore, to provide a novel method for permitting a lone worker in the field, not only to select an unused pair of tip and ring lines for use of the new subscriber's telephone, but also to conduct a test, remote from the central office, to determine whether or not the selected pair of lines are in an operative condition--i.e., have not been severed or shorted out.
Still another object of this invention is to provide for a novel method of the type described improved means for conducting a remote test of unused telephone lines prior to connecting the new subscriber's telephone to a selected pair of tip and ring lines, respectively.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawing.